<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    .cha {
      position: absolute;
      --size: 100px
    }

    .cha::before, .cha::after {
      content: '';
      position: absolute;
      background: red;
      height: 1px;
      width: var(--size);
      /*transform: rotate(45deg);*/
    }

    .cha::before {
      transform: rotate(45deg);
    }

    .cha::after {
      transform: rotate(-45deg);
    }
  </style>
</head>
<body style="padding: 200px">
<span class="cha"></span>
</body>
</html>
